Multiplexing (also known as muxing) is a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium. In digital television and digital radio systems, Digital Broadcast Multiplexes are well known entities that have been in existence for many years. These multiplexes exploit the fact that digital platforms have sufficient signal bandwidth to offer several channels (services) of programming within a single transmission. This transmission can then be de-multiplexed (un-mixed) at the reception point to allow specific channels to be viewed or recorded. Existing standards, such as those published by the Digital Video Broadcasting Project (DVB) and the Advanced Television Systems Committee (ATSC), specify in detail how these multiplexes work and how they fit into a larger broadcasting system.
Typically, digital broadcasting systems pack services such as source channels into multiplexes based upon coarse level parameters. Examples of such parameters are:
Longstanding contractual arrangements—for example, a large operator may have been sold an entire multiplex in order for them to make available a range of services;
To ensure a consistency of access to a set of services—for example, services which are being made available in the same region (or other similar criteria) may be placed within the same multiplex; and
Optimization of available capacity—for example, a multiplex may contain a mixture of high definition, standard definition and audio services which collectively make best use of the available bandwidth.
This service level of decision making behind the construction of multiplexes can generally be analyzed manually, by-hand as a one-off activity when the capacity is first brought on-stream. Hence, service level multiplex construction tends to be a legacy decision made at some point in the past.
The data flowing out of a Digital Broadcast Multiplex can also be subject to another established algorithm called Statistical Multiplexing in which service level parameters are varied in order to maintain a predefined goal when changes are made to the inputs of the multiplex. Most commonly, the quality of a target service may be maintained by balancing the target service quality against the quality of other services in view of dynamic changes in the complexity of each service. Commonly, statistical multiplexing algorithms in a digital broadcast environment alter the bandwidth allocated to services in order to more optimally pack them into the multiplex.
The following references are believed to represent the state of the art:
United Kingdom Patent GB 2 351 891 to NDS Limited;
United Kingdom Patent Application GB 2 408 433 to Nokia Corporation;
European Patent Application EP 1 811 726 to Alcatel USA Sourcing, L.P.;
United States Patent Application US 2006/0232706 to Curet et al.; and
International Patent Application. WO 99/55092 to Tiernan. Communications, Inc.